1. Technical Field of the Invention
The present invention relates to kinetic energy storage systems for use in moving vehicles. More particularly, the present invention relates to energy storage systems utilizing an integrated fly-wheel-motor-generator coupled to a system controller and further coupled to a drivetrain motor/generator for use in a hybrid vehicle.
2. Description of the Prior Art
While flywheels are well known in the art there has been little application of flywheels in moving vehicles. In particular, there has been little application of flywheels used as kinetic energy stores in automobiles. In spite of this lack of usage it is highly desirable to utilize flywheel systems to store kinetic energy and moving vehicles since they can be loaded and energy drawn many times. For example, a train equipped with a kinetic energy storing flywheel could serve a significant portion of that energy which was lost upon stopping the train. Similarly, the energy wasted in stopping an automobile, such as a bus or a taxi cab, could also be conserved and applied to accelerating the automobile for supplying the automobile with electrical power. Such a kinetic energy storage system could have vast application in the field of electric automobiles or electric-internal combustion hybrid automobiles.
The automobile environment however, presents special challenges in successful implementation of a flywheel to motor vehicle applications. Among these challenges is the need to deal with gyroscopic torques resulting from the vehicle""s angular motions and need to accommodate the translational accelerations of the vehicle. Additionally, several safety Issues resulting from the high energy and momentum stored in the flywheel also need to be taken into account, as does the difficulty of cooling the motor generator operating in a vacuum chamber. In addition, energy conservation considerations and user convenience dictate the requirement that the flywheel storage system possess a slow self-discharge rate.
While there have been many developments in flywheel technology in particular with respect to flywheel energy storage in a motor vehicle many of these developments have not overcome the aforementioned limitations in flywheel design. For example, U.S. Pat. No. 4,499,965 to Oetting et al. describes a hybrid drive arrangement utilizing a storage flywheel that allows a fast response to sudden increases in power demand while simultaneously providing for kinetic energy storage upon braking of the vehicle. However, as is common in most hybrid drive arrangements the flywheel is coupled separately to the vehicle crankshaft and the motor-generator which serves to store and/or transmit the energy inherent in the rotating flywheel. This arrangement entails separately manufactured flywheel disposed within a flywheel housing :which in turn is coupled to the motor generator. This standard design limits the packaging options within a hybrid vehicle in that the flywheel assembly and the motor-generator unit must be separately packaged. This inefficient packaging results in an increase in weight to the vehicle and the likely increase in the cost of assembly and maintenance of the vehicle.
Therefore, there is a need in the art for a flywheel assembly that is inexpensive, easily packaged, and adaptable for efficient use in a hybrid or electric vehicle drivetrain, for example, in a regenerative energy management system.
The present invention includes a novel regenerative energy management system having a flywheel assembly with an integrated motor-generator which is coupled to a drivetrain motor-generator. The coupling between the flywheel assembly and the drivetrain motor-generator includes a system controller having integrated voltage control and inverters. The present invention efficiently enables a vehicle to capture the kinetic energy resulting from a braking event storing this energy and then re-using the stored energy for subsequent acceleration.
For example, during a braking event most of the kinetic energy of a typical hybrid vehicle is converted to heat through the friction brakes. Conversely, the present system is designed to gather kinetic energy from a braking event utilizing the generator component of a drivetrain motor-generator unit. The resultant electrical current is transmitted to the system controller, where the current is modulated and distributed to a plurality of metal windings in the flywheel assembly. The current-carrying metal windings interact electromagnetically with a plurality of magnets joined to a flywheel within the flywheel assembly, such that the flywheel begins to rotate, thus storing that braking kinetic energy by spinning up the flywheel.
If the vehicle begins to accelerate, then stored kinetic energy can then be released using the generator portion of the integrated flywheel motor-generator. In this instance, the system controller inverts the flow of electrical current such that the magnets on the spinning flywheel electromagnetically induce a current in the metal windings within the flywheel assembly. The induced current is then distributed through the system controller where it is modulated and directed to the motor part of the drivetrain motor-generator which accelerates the vehicle.
In order to perform as described the present invention includes an inexpensive and optimized flywheel. Because a vehicle entering a braking event would generate a known kinetic energy the flywheel has a maximum rotational speed predetermined. Thus, the flywheel of the present invention avoids the use of expensive bearings, vacuum systems, cooling systems, and other such support subsystems found in other high technology flywheels. Because the flywheel is designed to have a maximum kinetic energy and a maximum rotational speed the moment of inertia of the flywheel may be optimized. By constraining the radius of the flywheel, an optimized shape that minimizes the flywheel mass while ensuring that the stress within the flywheel does not exceed safe bounds can be determined.
Secondly, the present invention includes the incorporation of a motor generator directly into the flywheel. The integration of the system saves valuable space within the vehicle, reduces the number of bearings necessary for operation, and simplifies the coupling of the flywheel motor generator to the flywheel.
Thirdly, the system controller having integrated inverters and voltage control determines the direction and flow of current between the flywheel assembly and the driveline motor-generator.